Esters of 4,4-di tert.butylperoxypentanoic acid as cross-linking initiators in the manufacture of copolymers of ethylene and other terminal ethylenically unsaturated monomers



United States Patent 2 s 5 Claims. (Cl. 26087.3)

ABSTRACT OF THE DISCLOSURE The present invention relates tocross-linking with new organic peroxides which are 3,3-ditert.butylperoxybutame-carboxylic acid esters, also known as esters of4,4- di tert.butylperoxypentanoic acid, wherein the ester moietycontains a hydrocarbon group having at most 20 carbon atoms, and whichare useful as peroxidic cross-linking initiators in the manufacture ofcopolymers of ethylene and monomers containing CHFCH groups. Theinvention also relates to the resulting cross-linked copolymericcompositions and to shaped articles made therefrom.

This application is a division of our copending application Ser. No.315,344, filed Oct. 10, 1963.

The present invention relates to the production of copolymers and isparticularly concerned with a process for cross-linking copolymers ofethylene and monomers containing CH =CH- groups with the aid of hithertounknown peroxidic cross-linking initiators. The invention also relatesto a process for preparing these new peroxides, as well as to the newperoxides per se.

In the cross-linking of copolymers of ethylene and monomers containingCH =CH groups, such as copolymers of (l) ethylene and propylene and of(2) ethylene and vinylacetate, etc., use is often made ofdicumylperoxide as an initiator. However, the use of this peroxide as aninitiator has the disadvantage that the finished products obtained byits use possess a disagreeable odor. As a consequence, peroxidicinitiators such as this cannot be used in many instances.

It has been found, surprisingly, that hitherto unknown peroxides of thegeneral formula in which R is a hydrocarbon group having at most 20carbon atoms, are very suitable initiators in the crosslinking ofcopolymers of ethylene and monomers containing CH =CH groups, becausethese peroxides do not give a disagreeable odor to the finishedcross-linked products and are almost equal in effectiveness to theperoxide most suited to this purpose, namely, dicumylper oxide, so faras their other properties are concerned.

The cross-linking of copolymers of ethylene with the aid of the novelperoxidic initiators according to the present invention may be carriedout in the usual apparatus diphenylguanidine.

3,409,600 Patented Nov. 5, 1968 under otherwise conventional conditionsof temperature and pressure, and if desired, in the presence ofconventional auxiliary agents such as carbon black, sulphur orsulphur-releasing compounds such as tetra-methylandtetra-ethylthiouramdisulphide, and accelerators such as The peroxides tobe used according to the present invention may be obtained by reactingtert.butylhydroperoxide, at a temperature of aryl-, aralkyl-, orcycloalkyl-ester of 3-ketobutane carboxylic acid in stoichiometricproportions, in the presence of an acid-reacting catalyst, andpreferably a mineral acid such as a solution of 70% by weight ofsulphuric acid in water, and eliminating the water formed during thereaction, plus any water that might be present in the starting material,plus the water in the sulphuric acid solution, by distillation with theaid of an added entrainer, or a suitable dehydrating agent, which maypreferably be anhydrous oxalic acid. In the latter case, this organicacid surprisingly acts simultaneously as a catalyst so that when.

present at the beginning, the use of the mineral acid is superfluous (asshown below in Example 3).

The alkyl-esters of 3-ketobutane carboxylic acid include both straightand branched chain alkyl-esters, especially the n-butylester and theZ-ethylhexylester; the aryl-esters including especially the phenylester;the aralkyl-esters including especially the benzylester; and thecycloalkyl esters including especially the cyclohexylester.

In order that the present invention in all of its ramifications may bestill more readily understood, the following specific examples aregiven. Where in these examples reference is made to compression, thiswas determined with the aid of the Williams plastimeter in the same Wayas described in S.P.E. Journal, 17 (1961) 265-270, but with the addedproviso that instead of a weight of 10 kg. a weight of 5 kg. was used.

Example 1 34.4 g. (0.2 mole) of 3-ketobutane carboxylic acid nbutylesterwere mixed with stirring, in a S-neckflask of 500 ml. capacity providedwith a mechanical stirrer, thermometer and water separator, with 36 g.(0.4 mole) of tert.butylhydroperoxide and with ml. of benzene as anentrainer. Thereafter, also with stirring within 1 minute 0.2 ml. ofsulphuric acid (70%) was added dropwise, care being taken that thetemperature of the reaction mixture was maintained at 25 "-30 C. Thewater of reaction, as well as the water present in the startingmaterial, was distilled otf azeotropically under reduced pressure duringthe reaction. After separation of the water in the water separator, thebenzene was recycled to the threeneckfiask.

After the reaction, the reaction mixture was freed from acid by washingsubsequently twice with 100 ml. of water, twice with 100 ml. of 2 NNaOH, and finally once again with 100 ml. of water.

After drying over sodium sulphate, the benzene was distilled off underreduced pressure at a final pot temperature of a maximum of 40 C.

68.3 g. of 3,3-di-tert.butylperoxybutanecarboxylic acid n-butylesterwere obtained, as follows:

Yield, 93%

Peroxide content, 91%

Active oxygen content, 8.72%

Example 2 20-35 C., with an alkyl-, I

butylperoxide as a carrier. Thereaften, 0.1 ml. of sulphuric acid (70%)was added dropwise with stirring within 1 minute, care being taken thatthe temperature of the reaction mixture was maintained at 25 30 C. Thewater of reaction, as well as 46.0 g. ,of-3.3-di-tert.butylperoxybutanecarboxylic acid n-butylester were obtainedin an analogous way, starting from 34.4 g. (0.2 mole) of3-ketobutanecarboxylic acid n-butylester, as follows:

the water present in the starting material, was eliminated from thereaction mixture during Peroxide content, 83% the reaction by distillingunder reduced pressure with the Active oxygen content, 7.95% aid of thedi-tert.butylperoxide. After separation of the 11 1.4306 water in thewater separator, the di-tert.butylperoxide was a recycled to theS-neckflask. The reaction mixture thus 10 WIth the various products thusobta1ned,-m1xtures"conobtained was freed from acid in the same manner asdetaining the following parts by weight were made up on a scribed inExample 1. mixing roll at a temperature of. 85 I A B o D E F o H, J KI L.M 1N.- Copolymer of ethylene and propylene contaimng 50% by weight ofethylene 100 100 100 100 100 100 100 100 Copolymer of ethylene andvinyl-acetate containing 45% by weight of vinylacetate 100 100 100 100100 HAF Carbon black 50 50 50 50 50 50 50 Dicumylperoxide Ester of3,3-di(tert.-butyl peroxy) butane carboxylic After drying over sodiumsulphate, the carrier was eliminated by distillation under reducedpressure at a final pot temperature of a maximum of 40 C. 104 g. of3,3-di-tert.buty1peroxybutanecarboxylic acid stearyl ester was obtained,as follows:

Yield, 87%

Peroxide content, 88%

Active oxygen content, 5.33%

Melting point after recrystallisation from methanol, 36-

The following peroxides were obtained in an analogous way:3,3-ditert.butylperoxybutanecarboxylic acid ethyl-, 2-ethylhexyl-,cyclohexyland benzyl-ester, respectively:

In a 3-neckflask of 500 ml. capacity provided with a mechanical stirrer,thermometer and reflux condenser, 19.8 g. (0.22 mole) of anhydrousoxalic acid were added by small increments with stirring to a mixture of28.8

g. (0.2 mole) of 3-ketobutanecarboxylic acid ethylester and 3.6 g. (0.4mole) of 100% tert.butylhydroperoxide, care being taken that thetemperature of the reaction mixture did not exceed C. The mixtureobtained was heated for 3 hours at 30 C. and subsequently cooled, withstirring, to room temperature. Subsequently the solid material presentin the reaction mixture was filtered off. The remaining clear solutionwas, after having been diluted with 100 ml. of benzene, freed from acidin the same way as described in Example 1.

After drying over sodium sulphate, the benzene was distilled off underreduced pressure at a final pot temperature of not more than C. 37.2 g.of 3.3-di-tert.butylperoxybutanecarboxylic acid ethylester wereobtained, as follows:

Peroxide content, 81% Active oxygen Content, 8.47% 11 1.4282

The mixtures thus obtained were cross-linked by working in a press at165 C. for a period of 40 minutes. After 30 minutes at a temperature ofC., the compression of samples from sheets thus obtained weredetermined. The results were as follows:

Sheet Compression Sheet Compression in percent in percent With theexception of sheets B and J, the sheets did not possess a disagreeableodor.

While specific examples of preferred methods embodying the presentinvention have been set forth above, it will be understood that manychanges and modifications may be made in the methods of procedurewithout departing from the spirit of the invention. It will therefore beunderstood that the examples cited and the particular proportions andmethods of operation set forth above are intended to be illustrativeonly, and are not intended to limit the scope of the invention.

What is claimed is:

1. In a process for cross-linking a copolymer of ethylene and a monomercontaining a CH =CH group with the aid of a peroxidic initiator, theimprovement comprising employing as an initiator a compound having thegeneral formula in which R is a hydrocarbon group having not more than20 carbon atoms.

2. A process as defined in claim 1, in which the cross linking iscarried out in the presence of at least one added auxiliary agent. i

3. An article comprising a cross-linked copolymer of ethylene and amonomer containing a CHQMCHQ group obtained by the process defined inclaim 1.

4. A new composition of matter comprising a copolymer of ethylene and amonomer containing a CHFCH group, and an organic compound having thegeneral formula in which R is a hydrocarbon group having not more than20 carbon atoms.

No references cited.

JOSEPH L. SCHOFER, Primary Examiner.

10 M. B. KURTZMAN, Assistant Examiner.

Notice of Adverse Decision in Interference In Interference No. 99,279,involving Patent No. 3,409,600, P. R. A. Maltha. and S. B. Tijssen,ESTERS OF 4,4-DI TERT. BUTYLPEROXYPENTA- NOIC ACID AS CROSS-LINKIN G INITIATORS IN THE MANUFAC- TURE OF COPOLYMERS OF ETHYLEN E AND OTHERTERMINAL ETHYLENICALLY UN SATURATED MONOMERS, final judgment adverse tothe patenteeswas rendered J an. 18, 1977, as to claims 3 and 4.

[Oficz'al Gazette May 5, 1.977.]

